1. Field of the Invention
The present invention relates to a method of manufacturing a printed wiring board and more particularly to a method of manufacturing a printed wiring board having pads pitched at narrow intervals for mounting parts.
2. Description of the Related Art
Conventionally, according to the solder resist processes of the type of printed wiring board shown in FIGS. 1 (a)-(d) and FIGS. 2 (a) and (b), after pads 2 for mounting parts are formed at desired positions in a circuit on an insulating board 1 by a forming process using etching resist 3 (FIG. 1 (a)), the etching resist 3 is peeled off (FIG. 1 (b)).
One side of the insulating board is then coated with photosolder resist 9 (FIG. 1(c)). The photosolder resist 9 is then dried to a tack-free state and subjected to a process in which the resist 9 is exposed to ultraviolet rays through a Mylar film serving as a photo mask (FIG. 1(d)) and then to a developing process to prepare a hardened solder resist 10 (FIG. 2 (a)).
Thereafter, the processes illustrated in FIG. 1 (c), 1 (d) and FIG. 2 (a) are repeatedly applied to the other side of the insulating board 1 to form a desired pattern of solder resist 9a (FIG. 2 (b)).
For the solder resist, a photosolder resist composed of a liquid crystal or a dry film and a thermosetting liquid solder resist are generally used.